Mobile Terminal (MT) subscribers increasingly rely on their MT for their communication and organizational needs. More recently, Push-to-Talk (PTT) technology over a cellular network, a Voice-Over IP (VoIP) network such as Session Initiated Protocol (SIP), or a Wireless Local Area Network (WLAN) has provided even more options for personal communications among groups of users. PTT provides users with instantaneous connections that bypass some of the more rigorous call establishment procedures associated with traditional MT calls.
Push-To-Talk (PTT) technology allows point-to-multipoint communications between users. Transmissions are usually half-duplex, and require a user to press and hold a button on the wireless communications device while speaking into a microphone. PTT is a technology that is most often associated with private radio systems and an operator of such radio systems may be interested in restricting MTs from PTT access on its network.
In a telecommunications network, certain information concerning a mobile station is stored in a home location register (HLR). The HLR is a database used to store and manage subscription information for mobile subscribers belonging to a specific telecommunications operator. A telephone company or telephone service provider is an example of what is meant by “telecommunications operator”. Typically, an HLR stores data about subscribers, including subscriber's Mobile Station International Subscriber Directory Number (MSISDN), International Mobile Subscriber Identity (IMSI), supplementary services, location information, and authentication parameters. The HLR may additionally store restriction information for limiting the subscriber's use of the MT to a specified geographical area. For example, the service may be restricted to one or more allowed cells. A service may be for a determination in which cells the MT can receives and originates calls. In particular, the MT is permitted to operate only in cells identified in the subscriber's record in the HLR. Thus, only applicable cells listed in the subscriber's record are paged when a call is directed to the mobile station, and the MT can only originate calls and sustain calls from such cells. Furthermore, calls originated and terminated by the mobile station calls in the applicable cells listed in the subscriber's record can be sustained when the mobile station travels into non-applicable cells.
Traditionally the radio transmissions of each Access Node (AN) of a telecommunications network cover a geographical area, e.g., one or more “cells”. A predetermined number of cells typically form a location area. When an active MT travels from an old cell to a new cell, a handoff or handover must occur from the access node handling the old cell to the access node handling the new cell. A MT in an idle mode can move or “roam” from an old cell to a new cell, and even change location areas.
Each access node is connected to one MSC 30. Typically, each MSC is connected to and serves a plurality of access nodes. The MSC is responsible for switching functions related to call processing for calls originated from and destined to a mobile station. Each MSC interfaces with access nodes which its serves, as well as interfacing with other switching stations. In particular, each MSC connects to non-mobile switching centers through a gateway mobile switching center (GMSC).
As the MT roams into a location area that is handled by a different MSC, a location update operation must occur so that both the HLR and the visitor location register (VLR), typically at a mobile switching center (MSC), have appropriate current information about the MT and its whereabouts. In this regard, when a MT roams into an area having a different location identifier, a forced registration typically occurs. In the forced registration, the HLR is updated regarding the particular MSC now serving the MT. The VLR is a database which contains information about MTs current location in the geographical area serviced by an associated MSC.
When the MT travels into an allowed cell of new location area, the geographical restriction information for the mobile subscriber is transmitted to the VLR. Using the geographical restriction information for the mobile subscriber stored at the VLR, the MSC currently handling the MT determines whether calls can be completed and processed. Roaming attempts outside the area of geographical restriction are permitted so that whereabouts of the MT can be monitored and maintained. However, except for soft restrictions, attempts to originate calls outside the area of geographical restriction are rejected. A geographical restriction may be based upon city or country borders. This method works fine for geographic restriction of services like PTT in a network comprising an HLR.
However, in a third generation (3G) telecommunication network or International Mobile Telecommunications-2000 (IMT 2000) like a Code Division Multiple Access 2000 First Evolution-Data Only (CDMA2000 1x EV-DO) there is no HLR and no MSC in the call chain. The CDMA2000 1x EV DO network rather comprises an access node (AN), a packet data service node (PDSN) and an AAA server for providing packet data service to a user of a MT. Thus, a subscriber profile lies in an AAA server. Therefore, in a CDMA2000 1x EV-DO network, there is no mechanism for an operator to restrict the use of PTT service in accordance to the geographic location of the mobile station.
For that reason, there is a need to provide a solution to prevent a MT to receive PTT service in a packet data telecommunications network. The invention provides a solution to this problem.